I searched for this first but couldnt come up with why my car is doing it. I have a new tensioner, all the pulleys are lined up and the belt lineup mark is a little to the left. When the car is idling the battery gauge is fine, then when i add the headlights it goes down and wiggles back and forth. Next when i add the vent it goes sooo far down to the left. When it rains my belt slips a ton, this all started happening like 2 months ago. Has anyone had a similar problem, or know what i can do to stop this.